Comander Perimeter Security System
Engineering and Installation Manual
Page 6 of 72
Ethernet switch, having both CAT5e and optical fibre connections. Copper CAT5e
connections are limited to about 100m, but by using the fibre connections, adjoining
Comanders can be spaced up to 1.5km apart.
1.2.1 Network Addressing
All Comander devices are supplied with factory-set MAC and IP addresses, for
Ethernet and IP network connection. Since the maximum number of Comanders on
any single network cannot exceed 20 (see section 2.1 below), a Comander network will
usually be a class C subnet.
Comander Racks must be configured with static IP addresses, and all devices which
connect using the Comander subnet should also be configured with static IP
addresses: DHCP should not be used to assign IP addresses to devices within the
Comander subnet. It should not normally be necessary to change the factory-
configured network settings, though it is possible to do so using the configuration
mechanisms described later in this manual.
The Comander Ethernet network can be used as a transport for other IP/Ethernet traffic
– for example, an IP camera network can be configured to run over the same physical
connections using a different subnet, with addresses allocated by a DHCP service if
required. However, it is important when designing such a system to consider the
network bandwidth and capacity. The Comander network runs at 100Mb/s, over
copper or fibre, so its ability to support multiple high-bandwidth devices (such as IP
cameras) is quite limited.
It may also be important to consider the Subnet Mask setting on a Comander carefully.
All Comanders in a system must be visible to each other, with the same IP range and
Subnet Mask setting. Sometimes a Subnet Mask will be configured to separate
Comanders from other devices (such as those handling CCTV IP traffic), as there is
normally no need for all connected Ethernet devices to communicate at an IP level.
But if the Comander's Network Topology feature is being used to monitor the integrity
of the network connections, that Comander's Subnet Mask must be set so that it can
communicate with all the devices whose IP addresses are listed in the Network
Topology page of the Configurator – see section 2.5.11 below for more information.
1.2.2 Ring Network Topology
A robust Comander network uses the Ethernet connections not only to communicate,
but also to monitor its own connections. This is achieved using a Ring network
topology, in conjunction with a monitoring and self-repair system called Rapid
Spanning Tree Protocol ("RSTP"). RSTP is normally enabled on one of the Comander
Racks - it ensures that any breaks in the network are detected automatically, and data
rerouted automatically via any other available connection to its destination.
Comander systems are usually designed to provide multiple redundant routes and
connections, to ensure that the RSTP can always find an alternative data path in the
event of failure or sabotage.
Rings are not a normal topology for Ethernet networking – CAT5e and fibre Ethernet
networks more usually use a star topology – but in conjunction with RSTP, the Ring
provides better fault-tolerance and detection than more conventional network
topologies.
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